A pervasive and fundamental source of literacy development, now competing with reading as the conventional medium for literacy acquisition, is the hundreds and even thousands of hours that young children spend playing computer games. These games have become increasingly sophisticated, representing, for example, simulation of micro-worlds (e.g., nation states in conflict, ecosystems) or complex physical systems (e.g., flight simulation). Experts in the game development field predict that this degree of sophistication will continue to increase dramatically in the coming years. Associated with this medium is the production of complex instruction manuals, web sites and interactive on-line communication between players. The objectives of this project are to determine the nature of conceptual development that potentially results from the large amount of time that many children invest in game interaction, with the goal of ultimately understanding how the pervasive medium of computer games impacts on the acquisition of cognitive skills. In particular, many games are sufficiently complex that they may encourage the development of planning skills or scientific reasoning. There are many genres of computer games, but two are of specific interest to us because they are good examples of sophisticated forms of simulation of complex interactions, one between a human operator and a modern machine governed by realistic physical principles, the other incorporating political rivalry and Machiavellian strategy among opposing factions. In an object manipulation game, such as Enigmo, relevant procedural knowledge includes basic principles of motion, gravity, and acceleration. We suggest that development of this form of knowledge can influence and likely improve reasoning about the influence of gravity on the movement of objects. In a game such as Civilization, development of planning, strategy, and situation models is involved. We plan to assess the nature of the cognitive skills acquired in the course of mastering complex computer games, and the relevance of these skills to literacy.